Process for preparation of high purity isobutylene

Abstract

Highly purified isobutylene, up to 99.9% pure, is obtained by treating a reaction mixture such as that recovered from an isobutylene-containing hydrocarbon mixture also containing an aqueous solution of an aliphatic carboxylic acid having 1 to 6 carbon atoms that has been reacted in an acidic ion exchanger and from which the unreacted hydrocarbons have been removed. The operative ingredients of the treated mixture are tertiary butyl alcohol, secondary butyl alcohol and their esters of the carboxylic acid employed. When treated with an acidic ion exchanger the carboxylic acid is first formed which inhibits the secondary butyl alcohol and secondary butyl ester of the acid from decomposing and high purity isobutylene is recovered therefrom by conventional distillation.

We claim: 
     
       1. A process for the preparation of high purity isobutylene comprising treating a mixture of tertiary butyl alcohol and a tertiary butyl ester of an aliphatic carboxylic acid having 1 to 6 carbon atoms in the presence of an acidic ion exchanger and separating isobutylene in a highly purified form by distillation. 
     
     
       2. A process for the preparation of isobutylene according to claim 1, wherein during the treatment in the presence of the acidic ion exchanger at least a part of the tertiary butyl alcohol in the mixture is not decomposed but remains as such in the mixture. 
     
     
       3. A process for the preparation of isobutylene according to claim 1 or 2, the mixture is treated in the presence of the acidic ion exchanger at a temperature of about 60 to about 120° C. under a pressure in the range of from atmospheric pressure to about 4.5 Kg/cm 2  G. 
     
     
       4. A process for the preparation of isobutylene according to claim 1, 2 or 3, wherein the acidic ion exchanger is positioned in the bottom portion of a distillation column for distilling and refining isobutylene formed by decomposition of said mixture. 
     
     
       5. A process for the preparation of isobutylene according to claim 1, wherein the mixture treated is a mixture of tertiary butyl alcohol and a tertiary butyl ester of an aliphatic carboxylic acid having 1 to 6 carbon atoms recovered from a liquid reaction mixture obtained by subjecting an isobutylene-containing hydrocarbon mixture to hydration reaction with an aqueous solution of an aliphatic carboxylic acid having 1 to 6 carbon atoms in the presence of an acidic ion exchanger. 
     
     
       6. A process for the preparation of isobutylene according to claim 1, 2, 3, 4 or 5, wherein the purity of the isobutylene product is at least 99.9%. 
     
     
       7. A process for preparing isobutylene at a purity of at least 99.9% consisting of: (i) treating an aqueous mixture of tertiary butyl alcohol and a tertiary butyl ester of a C 1  -C 4  carboxylic acid with an acid ion exchanger at a temperature in the range of about 60° C. to about 120° C. at a pressure from atmospheric to about 4.5 Kg/cm 2  G to produce an isobutylene-rich reaction gas; and   (2) distilling the thus obtained reaction gas and recovering high purity isobutylene therefrom.